Lightweight and buoyant fiber optic cables have many useful applications in an underwater environment. Remotely operated vehicles (ROVs), for example, may be tethered by a fiber optic cable. The fiber optic cable may include an optical fiber for transferring data and an electrical conductor for supplying electrical power to a remotely operated vehicle. The performance of these vehicles can be impaired by the drag and weight of the fiber optic cable.
Marine surface vessels may tow fiber optic cables for a variety of purposes, such as for sonar scanning and marine seismic surveying. It is often desirable to vary the depth at which each portion of a cable is towed. For example, in marine seismic surveying, one or more fiber optic cables (known as streamers) including hydrophones are towed by a vessel. The streamers may be several kilometers or more in length. In some applications, it may be desirable to maintain an entire length of the streamers in a horizontal position so that the hydrophones are towed at the same depth. Alternatively, some sections of the streamers may be maintained at shallower depths than other sections.
Small unmanned autonomous vehicles may tow cables coupled to sensors and communication buoys. These cables may be towed at fixed depths or even on a surface of the water. Similarly, the performance of these vehicles can be impaired by the drag and weight of the cable.
One approach to control the buoyancy of a fiber optic cable is to add material to the cable. While effective for controlling buoyancy, the added material causes the diameter of the fiber optic cable to change. If the diameter of the cable is significantly increased, for example, then the other components of the cable may have to be reengineered. Another disadvantage of increasing the diameter of the fiber optic cable means that the size of the spools used to store and transport the cable is increased as well.